Conventionally, a cellulose-containing fabric has been treated with cellulase to impart desired properties to the fabric. For example, in the textile industry, treatment with a cellulase is carried out to improve the touch feel and appearance of a cellulose-containing fabric, or to impart a “stonewash” appearance to a colored cellulose-containing fabric, thereby providing the fabric with localized color change [European Patent No. 307,564 (patent reference 1)].
It is known that, when the colored cellulose-containing fabric has been washed repeatedly, a fuzzing of the fabric occurs, which makes the color of the colored fabric unclear. The color of the colored fabric can be clarified by adding cellulase to a detergent to thereby remove the fuzz or to prevent the fuzz formation [European Patent No. 220,016 (patent reference 2), WO95/02675 (patent reference 3), WO97/30143 (patent reference 4), and WO98/08926 (patent reference 5)], and detergents containing cellulase are currently on the market, particularly in Western countries.
As to cellulases which may be contained in a detergent, it is known that, in detergents, a color clarification activity (i.e., an activity to remove fabric fuzz and clarify the color of the fabric) of a purified 43 kD endoglucanase component (EGV) derived from a microorganism belonging to genus Humicola was approximately 30 times that of a cellulase preparation containing plural conventional cellulase components [WO91/17243 (patent reference 6)]. Further, it is known that the color of a colored fabric can be clarified by reacting an endoglucanase NCE5 derived from a microorganism belonging to genus Humicola (hereinafter sometimes simply referred to as “NCE5”) with the colored fabric in a detergent [WO01/90375 (patent reference 7)]. Furthermore, it is known that, in detergents, the color clarification activity of culture liquid obtained by cultivating Humicola insolens in which an endoglucanase RCEI derived from a microorganism belonging to genus Rhizopus (hereinafter sometimes simply referred to as “RCEI”) was overexpressed was more than 20 times that of culture liquid obtained by cultivating Humicola insolens in which RCEI was not overexpressed [WO00/24879 (patent reference 8)].
As described above, it is known that various endoglucanases exhibit the color clarification activity, i.e., the activity to clarify the color of colored fabric, but there are few endoglucanases sufficiently exhibiting this activity when contained in detergents now on the Western market. It is considered that the inhibition or reduction of the activity in the detergents is caused by a large amount of anionic surfactants or builders contained in the detergents.
In addition, tap water used for washing in Western countries is generally hard, and contains a large amount of divalent cations, such as Ca2+ or Mg2+. Because the divalent cations drastically reduce a detergent activity of each surfactant contained in the detergents, the detergents contain one or more builders which adsorb the divalent cations [“Fragrance Journal”, 1995, vol. 11, p. 33-55 (non-patent reference 1)]. Further, because the hardness of tap water varies in accordance with countries or regions, the kind and/or the amount of the builders are appropriately selected in accordance with countries or regions. Furthermore, it is known that the divalent cations affect not only the detergent activity of the detergent, but also the cellulase activity [Mansfield, S. D. et al., “Enzyme Microb. Technol.” 23, 1998, p. 133-140 (non-patent reference 2), and Jenkins, C. C. AND Suberkropp, K., “Freshwater Biology”, vol. 33, No. 2, 1995, p. 245-253 (non-patent reference 3)]. Therefore, according to the hardness of water, a problem in which an inhibition of the cellulase activity reduces the color clarification activity to be desired, or a problem in which an enhancement of the cellulase activity reduces the strength of fabric, occurs.
Because the builder itself affects the cellulase activity, it is difficult to alleviate the effect of the hardness of water on the color clarification activity of the cellulase, by adding thereto the builder. Therefore, a cellulase not easily affected by the hardness of water and exhibiting a stable color clarification activity is desired.
Conventionally, cellulose-containing fabric is treated with a mixture of plural cellulase components, as a cellulose preparation. However, a large amount of cellulase is necessary to obtain a desired effect for the cellulose-containing fabric, and therefore, the development of the cellulose preparation has been retarded by the difficulty caused by this necessity. In many cases, a cellulase preparation is provided as a preparation comprising a large amount of endoglucanase having a high activity. As a process for preparing the cellulase preparation, processes for overexpressing a desired endoglucanase having a high activity in host cells, using genetic recombination techniques, are known [WO91/17243 (patent reference 6), WO98/03667 (patent reference 9), and WO98/11239 (patent reference 10)].
As preferable host cells used in the processes, there may be mentioned, for example, filamentous fungi belonging to Hyphomycetes, such as filamentous fungi belonging to Aspergillus, Humicola, or Trichoderma. As the host for preparing cellulase used in a detergent, the filamentous fungi belonging to Aspergillus or Humicola, which produce neutral cellulase, is preferable to those belonging to Trichoderma, which produce acidic cellulase, because the pH in the detergent is alkaline. Particularly, in view of the industrial production of the enzyme, the filamentous fungi belonging to Humicola having a high productivity is most preferable [WO01/90375 (patent reference 7) and WO98/03640 (patent reference 11)].
However, when a filamentous fungus belonging to Humicola is used to express a gene derived from a different species (i.e., exogenous gene), the expression is often inhibited because features in the nucleotide sequence of the gene (such as codon usage in the gene) are different. In this case, it is necessary to modify the exogenous gene. For example, when the endoglucanase RCEI derived from a microorganism belonging to genus Rhizopus belonging to Zygomycetes is overexpressed in Humicola insolens, the gene encoding RCEI should be optimized in accordance with the codon usage of the host cell [WO00/24879 (patent reference 8)]. However, if such an optimization is carried out, it will be difficult to express an exogenous gene as much as endogenous genes. Further, even when the enzyme of interest is expressed and produced in a host, it is anticipated that the enzyme is digested with proteases or the like contained in a culture liquid during cultivation to obtain the enzyme as digested products or partial fragments.    [patent reference 1] European Patent No. 307,564    [patent reference 2] European Patent No. 220,016    [patent reference 3] International Publication WO95/02675    [patent reference 4] International Publication WO97/30143    [patent reference 5] International Publication WO98/08926    [patent reference 6] International Publication WO91/17243    [patent reference 7] International Publication WO01/90375    [patent reference 8] International Publication WO00/24879    [patent reference 9] International Publication WO98/03667    [patent reference 10] International Publication WO98/11239    [patent reference 11] International Publication WO98/03640    [non-patent reference 1] “Fragrance Journal”, 1995, vol. 11, p. 33-55    [non-patent reference 2] Mansfield, S. D. et al., “Enzyme Microb. Technol.” 23, 1998, p. 133-140    [non-patent reference 3] Jenkins, C. C. AND Suberkropp, K., “Freshwater Biology”, vol. 33, No. 2, 1995, p. 245-253